The present invention relates to a Cu-containing Nb3Al multifilamentary superconductive wire and process for producing the same. More specifically, it relates to a Cu-containing Nb3Al multifilamentary superconductive wire which can be applied to generation of all magnetic fields of approximately 29 T or less, and a process for producing the same.
To alloy superconductors, an Nbxe2x80x94Ti wire has been so far actually used for a low magnetic field of up to 9 T (tesla) at 4.2 K, and an Nb3Sn or V3Ga wire for a high magnetic field of 9 to 21 T. On the other hand, an Nb3Al superconductive wire produced by a rapid heating/quenching and transformation method has been expected to be put to practical use by studies in recent years. Since this wire exhibits Jc which is three to five times as high as Jc of existing actual superconductive wires, the performance of superconductive application instruments such as a high magnetic field NMR spectrometer, a fusion reactor, a superconductive particle accelerator and SMES can be improved to a great extent. Accordingly, there is a possibility that it replaces the existing actual superconductive wires. FIG. 1 shows a flow chart of producing an Nb3Al wire by a rapid heating/quenching and transformation method. In this case, the rapid heating/quenching and transformation method is a method which comprises subjecting an Nb/Al superfine complex wire as a precursor wire to rapid heating and quenching to first form directly an Nbxe2x80x94Al bcc supersaturation solid solution in the wire, then conducting additional heat treatment at approximately 800xc2x0 C., and converting the bcc supersaturation solid solution formed into an A15 phase compound to produce a superconductive wire having quite high Jc characteristics (Japanese Patent Registration No. 2021986).
Further, the present invention have proposed the similar method of producing the superconductive wire which comprises, as shown in FIG. 2, subjecting a precursor complex wire obtained with Ge or Si-containing Al alloy to rapid heating and quenching to first form directly Nb3(Al, Ge) as an A15 phase compound having a low degree of crystal long-range order, then heat-treating the same at approximately 800xc2x0 C. to restore the crystal long-range order and obtain the Nb3(Al, Ge) superconductive wire as the A15 phase compound. In the Nb3(Al, Ge) superconductive wire obtained by this method, Tc and Hc2 (4.2 K) are greatly improved and Jc in a high magnetic field is high. Accordingly, the development of this wire as a superconductive wire for generation of a superhigh magnetic field of 23 to 29 T has proceeded (Japanese Patent Application No. 59907/1999). However, in this superconductive wire, Jc in the low magnetic field is not so high. Therefore, considering economics, it has to be used in combination with other superconductive wires having excellent characteristics in the low magnetic field.
A problem of the invention is to provide a superconductive wire which is free from a defect that Jc is low in a low magnetic field and which can be applied to generation of all magnetic fields of approximately 29 T or less and a process for producing the same. Another problem of the invention is to provide a superconductive wire having excellent Jc characteristics in a high magnetic field in comparison with an Nb3Al wire.
In order to solve these problems, the invention provides the following.
That is, the invention first provides a Cu-containing Nb3Al multifilamentary superconductive wire having a multifilamentary (superfine multi-core) structure that a large number of micro-complex cores each obtained by complexing a Cuxe2x80x94Al alloy containing Cu in an amount of more than 0.2 at. % and at most 10 at. % in Nb are embedded in Nb, Ta, and Nb alloy or a Ta alloy as a matrix, wherein in the micro-complex cores, an A15 phase compound structure is formed by rapid heating at a temperature of 1,700xc2x0 C. or more for 2 seconds or less and quenching to approximately room temperature, and further additionally heat-treated at a temperature of 650 to 900xc2x0 C. The invention second provides the superconductive wire of the first invention, wherein in the micro-complex cores, the Cuxe2x80x94Al alloy complexed in Nb has an average diameter of 1 xcexcm or less. The invention third provides the superconductive wire of the first invention, wherein the Cuxe2x80x94Al alloy complexed in Nb has a volume ratio to Nb of 1:2.5 to 1:3.5 in terms of a Cuxe2x80x94Al alloy:Nb ratio. The invention fourth provides the superconductive wire of any one of the first to third inventions, wherein Cu for stabilization is coated as an outermost layer. The invention fifth provides the superconductive wire of any one of the first to third inventions, wherein Cu for stabilization surrounded by a diffusion barrier layer made of Nb or Ta is mounted in the matrix. The invention sixth provides a process for producing the Cu-containing Nb3Al multifilamentary superconductive wire of any one of the first to third inventions, wherein the wire having the multifilamentary (superfine multi-core) structure is made to have a temperature of 1,700xc2x0 C. or more by rapid heating for 2 seconds or less, then quenched to approximately room temperature and thereafter additionally heat-treated at a temperature of 650 to 900xc2x0 C. The invention seventh provides the process of the sixth invention, wherein before or after the additional heat treatment, Cu for stabilization is coated on the surface of the wire. The invention eighth provides the process of the sixth invention, wherein before the rapid heating, Cu for stabilization surrounded by a diffusion barrier layer made of Nb or Ta is mounted in the matrix.